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New Zealand Veterinary Journal Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tnzv20
Aspects of lower respiratory tract disease in the horse H.G. Pearce
a
a
Faculty of Veterinary Science , Massey University , Palmerston North Published online: 23 Feb 2011.
To cite this article: H.G. Pearce (1979) Aspects of lower respiratory tract disease in the horse, New Zealand Veterinary Journal, 27:1-2, 1-4, DOI: 10.1080/00480169.1979.34584 To link to this article: http://dx.doi.org/10.1080/00480169.1979.34584
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
NEW ZEALAND VETERINARY JOURNAL
1979
Aspects of lower respiratory tract disease in the horse H. G. Pearce*
N.Z.ve/.J.27: /-4
ABSTRACT
Downloaded by [Selcuk Universitesi] at 00:15 23 January 2015
Lower respiratory tract disease is'probably more common than is generally thought and may be manifest without spectacular respiratory symptoms. This paper is concerned with obstructive pulmonary disease in the horse. The cause of the condition may not always be identifiable, but the effects of obstructive respi ratory disease may be a permanent impairment of pulmonary function. There are a variety oftechniques to aid in the diagnosis oflower respiratory tract disease, the principal ones being thorough examination of the chest, endoscopy and radiography. The final common denominator of respiratory disease is alveolar hypoxia, and failure to recognize this by over-exercise of such horses may lead to permanent alveolar damage. Recent developments in therapy are discussed and include the use of mucolytic and bronchospasmolytic drugs. INTRODUCTION
There is a strong tendency for both veterinary surgeons and laymen to dismiss apparently mild respiratory symptoms in the horse as having no importance. In horses referred to the Vete rinary Hospital at Massey University, respiratory and other symptoms related to respiratory tract disease are considerably more common and more serious than is generally believed (24).
chest, but the electronic amplified stethoscope** is better. although it requires practice in its use because it tends to ac centuate adventitious noises. It is advisable to examine the thorax in a systematic manner because there are occasions when focal abnormalities may be detected, and it is desirable to identify any extraneous sounds. The range of abnormal respiratory sounds varies considerably in intensity and distribution, and may also vary quite markedly at the same place at different times. Frequently, there is a distinct asymmetry in the sound auscultated on opposite sides of the chest, and this may be quite pronounced after moderate exercise. The sounds themselves may comprise apparently normal bronchial tones at the hilus of the lung, harsh dry rales, moist rales, or crackling sounds at some distance from the hilus. Pleuritic friction sounds are rarely heard even in the presence of severe pleuritis. Nasal exudates may, or may not, be present and knowledge of their absence should be kept in the correct perspective. The presence of nasal exudate indicates either a rhinitis or the production of exudates lower in the respiratory tree in excess of the animal's ability to remove them by swallowing. Epistaxis may accompany respiratory diseases, and one should consider the possibility of the blood originating from lesions in the lower respiratory tract.
HISTORY
Those horses referred to Massey with respiratory disease have a history that falls into one of two categories. The first category comprises animals that had histories of respiratory symptoms present for variable periods (in some cases since weaning). The second category includes those animals that had raced well for up to a mile, but stopped badly in the straight when confidently expected to run a good race. The latter group either had a previous history of respiratory disease, but were presumed to have recovered, or no history of respiratory disease whatsoever. Obviously, these two categories include all horses.
AETIOLOGY
There is usually no alteration to the cardinal signs, except in the a,cute stages of respiratory disease when there may be fever, rapid respiration. varying degrees of dyspnoea, and an increase in the heart and pulse rates. When obstructive respiratory di sease has been present for prolonged periods, there is usually a significant change in the character of respiration and the re spiratory sounds. Affected horses tend to have a degree of inspiratory dyspnoea with extreme dilation of the nostrils, and expiratory dyspnoea with a pronounced subcostal abdominal groove alone, or accompanied by a double expiratory movement. Most horses will have a cough, or make a variety of respiratory noises, which may suggest the presence oflaryngeal hemiplegia. There is usually no change to the lymph nodes of the head. On auscultation of the chest. there is usually an increase of the area over which respiratory sounds may be heard. This is a very important feature of lower respiratory tract disease. A conven tional clinical stethoscope is quite adequate to auscultate the
Frequently the veterinary surgeon is consulted at a relatively late stage of the disease, in which case he is concerned more with its effects than its cause. There are many respiratory virus infections in horses (9) (11) (20) (25). Their relative importance in respiratory disease in horses in this country is unknown, but it should be remembered that many of these infections are probably inevitable and are not normally fatal. The precise role of bacteria in lower respiratory disease is not clear, and we tend to speak glibly about secondary bacterial infection, often without a great deal of evidence to support it in individual cases. Other agents which have tended to be ignored are the fungi, helminth parasites, inert dust and noxious gases. In the case of fungi, the stable-environment probably provides ample scope for massive pulmonary infection, particularly when the stables are totally enclosed (10). Another aspect of pulmonary mycosis is the possibility of opportunistic fungal infections following an tibiotic therapy. Helminth parasites probably contribute a substantial insult to the lung, and it is common to encounter horses, particularly hacks and ponies on poor quality grazing, with a shallow soft cough and an eosinophilia. These'horses do not always have a high faecal strongyle egg-count, but respond very well to anthelmintic medication at high dose rates. Dust may act as a non-specific bronchial irritant which could initiate a cough reaction and exudation. This reaction, once started, could be the origin of progressive non-infectious pulmonary disease. There is little known about the role of various noxious gases in equine respiratory disease but, from experience gained with other species, it seems likely that the atmosphere in a
* Faculty ofYeterinary Science, Massey University, Palmerston No(lh.
** Meditron
CLINICAL EXAMINATION
Downloaded by [Selcuk Universitesi] at 00:15 23 January 2015
2 NEW ZEALAND VETERINARY JOURNAL VOL 27 poorly-drained and badly-ventilated horse-box could contain rulent or metazoan infection. Elevated plasma fibrinogen levels irritant gases such as ammonia and hydrogen sulphide (16). may indicate a chronic focus of infection. Finally, respiratory disease may be a sequel to surgery in which (3) Endoscopy. The examination is not complete unless the animal is laterally recumbent, causing over-perfusion and endoscopy is carried out. While the fibreoptic endoscope is a under-ventilation of the lowermost lung. very expensive instrument, the small rigid instruments still have a very important role in specialized equine practice. (4) DiagnostiC Medication. Reports from Germany have PATHOGENESIS shown that, in obstructive pulmonary disease, a temporary relief may follow the parenteral administration of atropine and cor There are two common denominators of respiratory disease. ticosteroid (23). The first is alveolar hypoxia which may arise from many causes. The second is pulmonary damage which may be sustained when (5) Radiography. The usefulness of radiography in clinical the animal is obliged to make good an oxygen debt. Perhaps the practice. as it relates to equine respiratory disease, is limited mainly by the costs involved. Unlike the large static units, most best way of attempting to explain the origins of alveolar damage, mobile X-ray machines do not have an output that is compatible and its subsequent effects, is to briefly describe the ventilation with short exposure times. Suitable radiographs can be taken if and perfusion of the normal equine lung and then describe the mechanism of the effects of obstructive respiratory disease. the animal is immobilised under general anaesthesia. At rest, ventilation and perfusion are restricted to the ventral The radiographic lesions that are seen are not always spec third of the lung. In response to anoxia, in whatever way it may tacular but, with practice and good quality plates, radiography may have considerable value, particularly for prognosis. In be induced. the normal lung is capable of a vast increase in general, the sites of close inspection are the walls of the bronchi, ventilation and perfusion because it offers minimal resistance to the flow of air and blood (7) (20). The equine alveolus is similar to the diameter of the bronchioles and their distribution across the lung field, and any evidence of interstitial scars. that in man. and has an extremely generous arterial blood supply (6) Cytology. Various techniques have been described (2) (19) (22). The venous supply to the alveolus, and its subsequent return (27) for obtaining, and assessing, qualitative and quantitative to the left side of the heart, is subject to local PC0 2 in the alveolus differences in the cells contained in lower respiratory mucus. so that, where alveolar hypercapnia occurs, the blood may be (7) Pulmonary function tests. Elaborate equipment has been shunted back into arterial circulation without having been re devised for the measurement of various equine respiratory oxygenated i.e. true venous admixture. Within the alveolar walls volumes (7) (13). In the absence of an equine research centre, or a the pores of Kohn allow the ready diffusion of gases from one suitable physiology unit, these procedures have academic in alveolus to another, as well as providing a relief valve for any terest only. increase in intra-alveolar air pressure. It would seem that the equine lung is well equipped to withstand insults that could limit gaseous exchange (4), and the fact that an animal manifests clinical symptoms should be regarded as evidence of a severe TREATMENT AND MANAGEMENT impediment to this function. A secondary consideration is the generous blood supply - and thickness of the pleura would seem In general, the medications that may be used fall into the to explain the infrequency of clinical pleuritis. following categories:Obstruction of an airway can be described simply as follows: if, for argument's sake, a total intake of 40 litres of air were Cough suppressants distributed symmetrically, 20 litres would flow into each lung. The principal factor determining the use of these drugs is Obstruction to airflow such as tumours, abscesses, bronchial whether, or not, the cough is productive. Clearly, if the cough is exudate, external pressures such as unilateral pneumo/hydro productive, suppression would simply delay the clearing me thorax, oedema of the mucosa and bronchial spasm would divert chanisms of the lung and prolong the convalescent period. One the air asymmetrically, so that one lung would become over of the dangers of using this group of drugs is that they tend to distended and the other would tend to collapse. Air flow create a false sense of security, and may encourage the owner to becomes turbulent as the diameter of the airway increases, so work the horse beyond its respiratory capacity. If exudate has that the normal lung tends to become both hyper-resonant and partially blocked a bronchiole, furtherdamangc could be caused noisier than the diseased lung. At the same time, there may be to the lung. Provided that these drugs are recognized to have substantial, local, air-pressure changes within the lung at dif symptomatic value. their use, in conjunction with rest and other ferent stages of the respiratory cycle (7) (13) (23). Add to this, the therapy, is justifiable. effects of coughing, and the possibility of a lowered threshold to the afferent limb of the Hering-Breuer reflex, and it is clear that Expectorants/ decongestants The traditional expectorants in equine medicine are the there is ample opportunity for severe lung damage. iodides, administered orally or intravenously. Alone, these Once the damage has been done to the alveolus, fibrosis occurs compounds have limited value but, in conjunction with other and, if the cause persists, there must come a time when there is medication, may be quite useful. The use of nebulizers to an irreversible impairment to pulmonary function. At rest, the provide a medicated atmosphere for a prolonged period has animal might well appear to be normal, but the oxygen debt received little attention in veterinary medicine. The spectacular incurred during strenuous exertion might impose dramatic symptomatic relief they offer the human patient might well be restrictions on the animal's performance. The basis of these achieved for horses. Compounds such as benzoin, eucalyptus, restrictions is apparent from the work of Gillespie and Tyler and others 17 )(13)(14)(18). menthol. and methyl salicylate could be used in a simple ap paratus to generate a medicated atmosphere. Fire could be a DIAGNOSTIC AIDS hazard, but this may be avoided by using an electric kettle connected by a pipe from its spout to a partially-sealed box. The most important diagnostic aids are visual appraisal and auscultation carried out at the initial clinical examination. A ntimicrobial therapy (1) A uscultation. Practice is all that is required. Without a specific aetiological diagnosis and antibiotic sen sitivity testing the use of antibiotics in respiratory disease is, at (2) Haematofogy. Note any changes in the total and differential leucocyte count to indicate the presence of a pubest, empirical and may even bc harmful. Tetracyclines are
Downloaded by [Selcuk Universitesi] at 00:15 23 January 2015
1979
NEW ZEALAND VETERINARY JOURNAL
contraindicated in the horse because of their tendency to induce diarrhoea(28). Human clinical investigations have shown that bronchial mucus contains three types of fibres that contribute to mucus viscosity. In purulent infection, there is acid mucopoly saccharide and deoxyribonucleic acid (DNA) whereas, in sterile mucus, the fibres comprise mucopolysaccharide and mucoprotein(29). Removal of the DNA fibres is achieved by a fibrolytic process mediated by enzymes released by leucocytes, or by the inhala tion ofDNA-ase therapeuticallY8). Removal of the DNA fibres does not, however, reduce the viscosity of bronchial mucus. Mucopolysaccharide fibres, which are increased in amount in purulent bronchial infections, are digested by bacterial exo enzymes, then removed by phagocytosis, and it may be contrary to the patient's interests to remove the source of these exo enzymes(6). A case for using antibiotics can be made, provided that they are administered in conjunction with a suitable ex pectorant, or mucolytic agent, such as Bisolvon*. A further consideration is to administer the antibiotic in such a way as to provide high local concentrations of the drug in bronchial mucus. The high cost precludes the use of antiviral chemotherapy, e.g. amantadine HCl, except in those cases in which a definite diagnosis of equine influenza had been made. Fungi may act as primary or secondary pathogens of the lung and fungicidal, or fungistatic, drugs may have therapeutic value. A recent respiratory case, previously treated with penicillin and streptomycin, yielded a pure culture of Aspergillus spp. that responded well to a combination of oral Bisolvon and potassium iodide. Other drugs which may be of value are the oral systemic fungicides Griseofulvin+ and Nystatin++. Sulfonamides may be more effective than antibiotics by virtue of their bacteriostatic effects. Their use in respiratory diseases of various species is well justified because they are readily absorbed when administered orally, and are known to diffuse quite readily throughout the body. Bronchodilators Those drugs which increase the lumen of an airway by reducing broncho-spasm, by the removal of exudates, or by the relief of oedema of the mucosa, may have considerable value in therapy. Bisolvon has been shown to be a bronchodilator in experimentally-induced bronchospasm in the guinea-pig, and part of its beneficial effects is attributed to this activity. Other bronchodilators are the so-called, aspirin-like group which in hibits the effects of prostaglandins E, and E 1 . Recent inves tigations have shown that, in a number of experimental and clinical situations, acute asthmatic-like symptoms may be al leviated by members of this groupO). The precise mode of action has not been fully elucidated, but it appears that the effects of the prostaglandins on smooth muscle and bronchial secretions is mediated by the kinin substances(l). When acute respiratory symptoms occur that are not accompanied by major changes in the sound auscultated in the chest or in the radiographic ap pearance of the bronchial wall, they may be due to broncho spasm in the so-called quiet zone at the level of the 18th-20th generation of bronchioles. The prostaglandin inhibitors are: aspirin, indomethacin, phenylbutazone, diethylcarbamazine citrate (Franocide - Bur roughs Wellcome), meclophenamic acid (Arquel- Parke Davis), sodium meclophenamate, and fluphenanate (Upjohn). The role of all of these drugs in dealing with respiratory symptoms, particularly acute symptoms, has not been tested clinically, but Franocide is well known for its effects in allergic respiratory disease, such as fog fever in cattle. +
+
Mycostatin - Squibb
• Boehringer Ingelheim
+ Fulcin - leI
3
The referral clinic at Massey deals with more chronic than acute respiratory diseases, but It is hoped that a clinical trial of these drugs can be instituted in the near future, once some toxicological data are available to reassure us that their use is safe. It would be premature to advise the use of this group of drugs until more information is available, but they seem to have a promising future. Mucolytic Drugs Bisolvon has been shown to be a potent mucolytic agent in clinical trials in various species. Trials. conducted here, have confirmed that the drug is valuable in lower respiratory disease of the horse(24). The drug is available for oral, or parenteral, administration and, in the latter case, is best given intnivenously. Dramatic clinical improvement has followed its use in a series of cases treated during the past 2 years at the Large Animal Clinic at Massey University. Alkali/Buffers Many patients could be suffering from a respiratory acidosis, if one considers the pathogenesis of alveolar hypercapnia, and the symptoms that accompany it. Oral administration of alkaline preparations, or various buffers, used clinically could be quite valuable in the short-term treatment of obstructive bronchial disease. On the other hand, prolonged hyper-ventilation could induce a marked respiratory alkalosis, so it would be advisable to determine the pH of plasma before starting this treatment. Potassium Salts In the human patient with chronic respiratory disease, it has been shown that there is a marked depletion in intracellular potassium, and that the oral administration of potassium salts is indicated. This loss of potassium can be expected in conditions of respiratory alkalosis, and may partially explain some of the effects of chronic respiratory disease. In view of the fact that plasma potassium levels are generally stable within phy siologicallimits, routine measurement of this element in plasma would not show any apparent abnormality, even when there was a marked loss of potassium. Rest Although there may be an impressive array of treatments available, rest is also important in the management of patients with respiratory disease. Rest means that the patient should not be exercised to the extent that an oxygen debt is incurred. If aM. oxygen debt is incurred, the dyspnoea that accompanies it may cause further alveoiardamage, with the possibility of permanent impairment of pulmonary function. The ideal situation is complete rest, but a horse at an advanced stage of training represents a financial outlay that few owners and trainers are prepared to forfeit. Under these circumstances, the best com promise is to advise continuati6n of light work in the form of extensive walking and trotting. Stable Hygiene The role of fungi, inert particles and noxious gases has been mentioned in the aetiology of respiratory disease. It is worthwhile to improve stable ventilation and minimize the irritation these agents may cause. Fungal growth in peat and sawdust bedding, for example, can cause an acute respiratory reaction in horses which may be prevented by spraying the bedding with copper sulphate solution (Littlejohn (1975), pers. comm.). The ventilation requirements for stables have been described by Sainsbury
New Zealand Veterinary Journal Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tnzv20
Aspects of lower respiratory tract disease in the horse H.G. Pearce
a
a
Faculty of Veterinary Science , Massey University , Palmerston North Published online: 23 Feb 2011.
To cite this article: H.G. Pearce (1979) Aspects of lower respiratory tract disease in the horse, New Zealand Veterinary Journal, 27:1-2, 1-4, DOI: 10.1080/00480169.1979.34584 To link to this article: http://dx.doi.org/10.1080/00480169.1979.34584
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
NEW ZEALAND VETERINARY JOURNAL
1979
Aspects of lower respiratory tract disease in the horse H. G. Pearce*
N.Z.ve/.J.27: /-4
ABSTRACT
Downloaded by [Selcuk Universitesi] at 00:15 23 January 2015
Lower respiratory tract disease is'probably more common than is generally thought and may be manifest without spectacular respiratory symptoms. This paper is concerned with obstructive pulmonary disease in the horse. The cause of the condition may not always be identifiable, but the effects of obstructive respi ratory disease may be a permanent impairment of pulmonary function. There are a variety oftechniques to aid in the diagnosis oflower respiratory tract disease, the principal ones being thorough examination of the chest, endoscopy and radiography. The final common denominator of respiratory disease is alveolar hypoxia, and failure to recognize this by over-exercise of such horses may lead to permanent alveolar damage. Recent developments in therapy are discussed and include the use of mucolytic and bronchospasmolytic drugs. INTRODUCTION
There is a strong tendency for both veterinary surgeons and laymen to dismiss apparently mild respiratory symptoms in the horse as having no importance. In horses referred to the Vete rinary Hospital at Massey University, respiratory and other symptoms related to respiratory tract disease are considerably more common and more serious than is generally believed (24).
chest, but the electronic amplified stethoscope** is better. although it requires practice in its use because it tends to ac centuate adventitious noises. It is advisable to examine the thorax in a systematic manner because there are occasions when focal abnormalities may be detected, and it is desirable to identify any extraneous sounds. The range of abnormal respiratory sounds varies considerably in intensity and distribution, and may also vary quite markedly at the same place at different times. Frequently, there is a distinct asymmetry in the sound auscultated on opposite sides of the chest, and this may be quite pronounced after moderate exercise. The sounds themselves may comprise apparently normal bronchial tones at the hilus of the lung, harsh dry rales, moist rales, or crackling sounds at some distance from the hilus. Pleuritic friction sounds are rarely heard even in the presence of severe pleuritis. Nasal exudates may, or may not, be present and knowledge of their absence should be kept in the correct perspective. The presence of nasal exudate indicates either a rhinitis or the production of exudates lower in the respiratory tree in excess of the animal's ability to remove them by swallowing. Epistaxis may accompany respiratory diseases, and one should consider the possibility of the blood originating from lesions in the lower respiratory tract.
HISTORY
Those horses referred to Massey with respiratory disease have a history that falls into one of two categories. The first category comprises animals that had histories of respiratory symptoms present for variable periods (in some cases since weaning). The second category includes those animals that had raced well for up to a mile, but stopped badly in the straight when confidently expected to run a good race. The latter group either had a previous history of respiratory disease, but were presumed to have recovered, or no history of respiratory disease whatsoever. Obviously, these two categories include all horses.
AETIOLOGY
There is usually no alteration to the cardinal signs, except in the a,cute stages of respiratory disease when there may be fever, rapid respiration. varying degrees of dyspnoea, and an increase in the heart and pulse rates. When obstructive respiratory di sease has been present for prolonged periods, there is usually a significant change in the character of respiration and the re spiratory sounds. Affected horses tend to have a degree of inspiratory dyspnoea with extreme dilation of the nostrils, and expiratory dyspnoea with a pronounced subcostal abdominal groove alone, or accompanied by a double expiratory movement. Most horses will have a cough, or make a variety of respiratory noises, which may suggest the presence oflaryngeal hemiplegia. There is usually no change to the lymph nodes of the head. On auscultation of the chest. there is usually an increase of the area over which respiratory sounds may be heard. This is a very important feature of lower respiratory tract disease. A conven tional clinical stethoscope is quite adequate to auscultate the
Frequently the veterinary surgeon is consulted at a relatively late stage of the disease, in which case he is concerned more with its effects than its cause. There are many respiratory virus infections in horses (9) (11) (20) (25). Their relative importance in respiratory disease in horses in this country is unknown, but it should be remembered that many of these infections are probably inevitable and are not normally fatal. The precise role of bacteria in lower respiratory disease is not clear, and we tend to speak glibly about secondary bacterial infection, often without a great deal of evidence to support it in individual cases. Other agents which have tended to be ignored are the fungi, helminth parasites, inert dust and noxious gases. In the case of fungi, the stable-environment probably provides ample scope for massive pulmonary infection, particularly when the stables are totally enclosed (10). Another aspect of pulmonary mycosis is the possibility of opportunistic fungal infections following an tibiotic therapy. Helminth parasites probably contribute a substantial insult to the lung, and it is common to encounter horses, particularly hacks and ponies on poor quality grazing, with a shallow soft cough and an eosinophilia. These'horses do not always have a high faecal strongyle egg-count, but respond very well to anthelmintic medication at high dose rates. Dust may act as a non-specific bronchial irritant which could initiate a cough reaction and exudation. This reaction, once started, could be the origin of progressive non-infectious pulmonary disease. There is little known about the role of various noxious gases in equine respiratory disease but, from experience gained with other species, it seems likely that the atmosphere in a
* Faculty ofYeterinary Science, Massey University, Palmerston No(lh.
** Meditron
CLINICAL EXAMINATION
Downloaded by [Selcuk Universitesi] at 00:15 23 January 2015
2 NEW ZEALAND VETERINARY JOURNAL VOL 27 poorly-drained and badly-ventilated horse-box could contain rulent or metazoan infection. Elevated plasma fibrinogen levels irritant gases such as ammonia and hydrogen sulphide (16). may indicate a chronic focus of infection. Finally, respiratory disease may be a sequel to surgery in which (3) Endoscopy. The examination is not complete unless the animal is laterally recumbent, causing over-perfusion and endoscopy is carried out. While the fibreoptic endoscope is a under-ventilation of the lowermost lung. very expensive instrument, the small rigid instruments still have a very important role in specialized equine practice. (4) DiagnostiC Medication. Reports from Germany have PATHOGENESIS shown that, in obstructive pulmonary disease, a temporary relief may follow the parenteral administration of atropine and cor There are two common denominators of respiratory disease. ticosteroid (23). The first is alveolar hypoxia which may arise from many causes. The second is pulmonary damage which may be sustained when (5) Radiography. The usefulness of radiography in clinical the animal is obliged to make good an oxygen debt. Perhaps the practice. as it relates to equine respiratory disease, is limited mainly by the costs involved. Unlike the large static units, most best way of attempting to explain the origins of alveolar damage, mobile X-ray machines do not have an output that is compatible and its subsequent effects, is to briefly describe the ventilation with short exposure times. Suitable radiographs can be taken if and perfusion of the normal equine lung and then describe the mechanism of the effects of obstructive respiratory disease. the animal is immobilised under general anaesthesia. At rest, ventilation and perfusion are restricted to the ventral The radiographic lesions that are seen are not always spec third of the lung. In response to anoxia, in whatever way it may tacular but, with practice and good quality plates, radiography may have considerable value, particularly for prognosis. In be induced. the normal lung is capable of a vast increase in general, the sites of close inspection are the walls of the bronchi, ventilation and perfusion because it offers minimal resistance to the flow of air and blood (7) (20). The equine alveolus is similar to the diameter of the bronchioles and their distribution across the lung field, and any evidence of interstitial scars. that in man. and has an extremely generous arterial blood supply (6) Cytology. Various techniques have been described (2) (19) (22). The venous supply to the alveolus, and its subsequent return (27) for obtaining, and assessing, qualitative and quantitative to the left side of the heart, is subject to local PC0 2 in the alveolus differences in the cells contained in lower respiratory mucus. so that, where alveolar hypercapnia occurs, the blood may be (7) Pulmonary function tests. Elaborate equipment has been shunted back into arterial circulation without having been re devised for the measurement of various equine respiratory oxygenated i.e. true venous admixture. Within the alveolar walls volumes (7) (13). In the absence of an equine research centre, or a the pores of Kohn allow the ready diffusion of gases from one suitable physiology unit, these procedures have academic in alveolus to another, as well as providing a relief valve for any terest only. increase in intra-alveolar air pressure. It would seem that the equine lung is well equipped to withstand insults that could limit gaseous exchange (4), and the fact that an animal manifests clinical symptoms should be regarded as evidence of a severe TREATMENT AND MANAGEMENT impediment to this function. A secondary consideration is the generous blood supply - and thickness of the pleura would seem In general, the medications that may be used fall into the to explain the infrequency of clinical pleuritis. following categories:Obstruction of an airway can be described simply as follows: if, for argument's sake, a total intake of 40 litres of air were Cough suppressants distributed symmetrically, 20 litres would flow into each lung. The principal factor determining the use of these drugs is Obstruction to airflow such as tumours, abscesses, bronchial whether, or not, the cough is productive. Clearly, if the cough is exudate, external pressures such as unilateral pneumo/hydro productive, suppression would simply delay the clearing me thorax, oedema of the mucosa and bronchial spasm would divert chanisms of the lung and prolong the convalescent period. One the air asymmetrically, so that one lung would become over of the dangers of using this group of drugs is that they tend to distended and the other would tend to collapse. Air flow create a false sense of security, and may encourage the owner to becomes turbulent as the diameter of the airway increases, so work the horse beyond its respiratory capacity. If exudate has that the normal lung tends to become both hyper-resonant and partially blocked a bronchiole, furtherdamangc could be caused noisier than the diseased lung. At the same time, there may be to the lung. Provided that these drugs are recognized to have substantial, local, air-pressure changes within the lung at dif symptomatic value. their use, in conjunction with rest and other ferent stages of the respiratory cycle (7) (13) (23). Add to this, the therapy, is justifiable. effects of coughing, and the possibility of a lowered threshold to the afferent limb of the Hering-Breuer reflex, and it is clear that Expectorants/ decongestants The traditional expectorants in equine medicine are the there is ample opportunity for severe lung damage. iodides, administered orally or intravenously. Alone, these Once the damage has been done to the alveolus, fibrosis occurs compounds have limited value but, in conjunction with other and, if the cause persists, there must come a time when there is medication, may be quite useful. The use of nebulizers to an irreversible impairment to pulmonary function. At rest, the provide a medicated atmosphere for a prolonged period has animal might well appear to be normal, but the oxygen debt received little attention in veterinary medicine. The spectacular incurred during strenuous exertion might impose dramatic symptomatic relief they offer the human patient might well be restrictions on the animal's performance. The basis of these achieved for horses. Compounds such as benzoin, eucalyptus, restrictions is apparent from the work of Gillespie and Tyler and others 17 )(13)(14)(18). menthol. and methyl salicylate could be used in a simple ap paratus to generate a medicated atmosphere. Fire could be a DIAGNOSTIC AIDS hazard, but this may be avoided by using an electric kettle connected by a pipe from its spout to a partially-sealed box. The most important diagnostic aids are visual appraisal and auscultation carried out at the initial clinical examination. A ntimicrobial therapy (1) A uscultation. Practice is all that is required. Without a specific aetiological diagnosis and antibiotic sen sitivity testing the use of antibiotics in respiratory disease is, at (2) Haematofogy. Note any changes in the total and differential leucocyte count to indicate the presence of a pubest, empirical and may even bc harmful. Tetracyclines are
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1979
NEW ZEALAND VETERINARY JOURNAL
contraindicated in the horse because of their tendency to induce diarrhoea(28). Human clinical investigations have shown that bronchial mucus contains three types of fibres that contribute to mucus viscosity. In purulent infection, there is acid mucopoly saccharide and deoxyribonucleic acid (DNA) whereas, in sterile mucus, the fibres comprise mucopolysaccharide and mucoprotein(29). Removal of the DNA fibres is achieved by a fibrolytic process mediated by enzymes released by leucocytes, or by the inhala tion ofDNA-ase therapeuticallY8). Removal of the DNA fibres does not, however, reduce the viscosity of bronchial mucus. Mucopolysaccharide fibres, which are increased in amount in purulent bronchial infections, are digested by bacterial exo enzymes, then removed by phagocytosis, and it may be contrary to the patient's interests to remove the source of these exo enzymes(6). A case for using antibiotics can be made, provided that they are administered in conjunction with a suitable ex pectorant, or mucolytic agent, such as Bisolvon*. A further consideration is to administer the antibiotic in such a way as to provide high local concentrations of the drug in bronchial mucus. The high cost precludes the use of antiviral chemotherapy, e.g. amantadine HCl, except in those cases in which a definite diagnosis of equine influenza had been made. Fungi may act as primary or secondary pathogens of the lung and fungicidal, or fungistatic, drugs may have therapeutic value. A recent respiratory case, previously treated with penicillin and streptomycin, yielded a pure culture of Aspergillus spp. that responded well to a combination of oral Bisolvon and potassium iodide. Other drugs which may be of value are the oral systemic fungicides Griseofulvin+ and Nystatin++. Sulfonamides may be more effective than antibiotics by virtue of their bacteriostatic effects. Their use in respiratory diseases of various species is well justified because they are readily absorbed when administered orally, and are known to diffuse quite readily throughout the body. Bronchodilators Those drugs which increase the lumen of an airway by reducing broncho-spasm, by the removal of exudates, or by the relief of oedema of the mucosa, may have considerable value in therapy. Bisolvon has been shown to be a bronchodilator in experimentally-induced bronchospasm in the guinea-pig, and part of its beneficial effects is attributed to this activity. Other bronchodilators are the so-called, aspirin-like group which in hibits the effects of prostaglandins E, and E 1 . Recent inves tigations have shown that, in a number of experimental and clinical situations, acute asthmatic-like symptoms may be al leviated by members of this groupO). The precise mode of action has not been fully elucidated, but it appears that the effects of the prostaglandins on smooth muscle and bronchial secretions is mediated by the kinin substances(l). When acute respiratory symptoms occur that are not accompanied by major changes in the sound auscultated in the chest or in the radiographic ap pearance of the bronchial wall, they may be due to broncho spasm in the so-called quiet zone at the level of the 18th-20th generation of bronchioles. The prostaglandin inhibitors are: aspirin, indomethacin, phenylbutazone, diethylcarbamazine citrate (Franocide - Bur roughs Wellcome), meclophenamic acid (Arquel- Parke Davis), sodium meclophenamate, and fluphenanate (Upjohn). The role of all of these drugs in dealing with respiratory symptoms, particularly acute symptoms, has not been tested clinically, but Franocide is well known for its effects in allergic respiratory disease, such as fog fever in cattle. +
+
Mycostatin - Squibb
• Boehringer Ingelheim
+ Fulcin - leI
3
The referral clinic at Massey deals with more chronic than acute respiratory diseases, but It is hoped that a clinical trial of these drugs can be instituted in the near future, once some toxicological data are available to reassure us that their use is safe. It would be premature to advise the use of this group of drugs until more information is available, but they seem to have a promising future. Mucolytic Drugs Bisolvon has been shown to be a potent mucolytic agent in clinical trials in various species. Trials. conducted here, have confirmed that the drug is valuable in lower respiratory disease of the horse(24). The drug is available for oral, or parenteral, administration and, in the latter case, is best given intnivenously. Dramatic clinical improvement has followed its use in a series of cases treated during the past 2 years at the Large Animal Clinic at Massey University. Alkali/Buffers Many patients could be suffering from a respiratory acidosis, if one considers the pathogenesis of alveolar hypercapnia, and the symptoms that accompany it. Oral administration of alkaline preparations, or various buffers, used clinically could be quite valuable in the short-term treatment of obstructive bronchial disease. On the other hand, prolonged hyper-ventilation could induce a marked respiratory alkalosis, so it would be advisable to determine the pH of plasma before starting this treatment. Potassium Salts In the human patient with chronic respiratory disease, it has been shown that there is a marked depletion in intracellular potassium, and that the oral administration of potassium salts is indicated. This loss of potassium can be expected in conditions of respiratory alkalosis, and may partially explain some of the effects of chronic respiratory disease. In view of the fact that plasma potassium levels are generally stable within phy siologicallimits, routine measurement of this element in plasma would not show any apparent abnormality, even when there was a marked loss of potassium. Rest Although there may be an impressive array of treatments available, rest is also important in the management of patients with respiratory disease. Rest means that the patient should not be exercised to the extent that an oxygen debt is incurred. If aM. oxygen debt is incurred, the dyspnoea that accompanies it may cause further alveoiardamage, with the possibility of permanent impairment of pulmonary function. The ideal situation is complete rest, but a horse at an advanced stage of training represents a financial outlay that few owners and trainers are prepared to forfeit. Under these circumstances, the best com promise is to advise continuati6n of light work in the form of extensive walking and trotting. Stable Hygiene The role of fungi, inert particles and noxious gases has been mentioned in the aetiology of respiratory disease. It is worthwhile to improve stable ventilation and minimize the irritation these agents may cause. Fungal growth in peat and sawdust bedding, for example, can cause an acute respiratory reaction in horses which may be prevented by spraying the bedding with copper sulphate solution (Littlejohn (1975), pers. comm.). The ventilation requirements for stables have been described by Sainsbury
